Microwave dryer for drying the glue line in paper forms



July 22, 1969 w. A. CUMMING ET AL 3,456,355

MICROWAVE DRYER FOR DRYING THE GLUE LINE IN PAPER FORMS Filed Nov. 22, 1967 3 Sheets-Sheet 1 FIG.

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MICROWAVE DRYER FOR DRYING THE GLUE LINE IN PAPER FORMS Filed Nov. 22; 1967 s Sheets-Sheet 2 lNvf/vfoflS Will/Alf A CuHfl/ms w/umn 84:91am. 67

July 22, 1969 w. A. CUMMING ET AL 3,456,355

MICROWAVE DRYER FOR DRYING THE GLUE LINE IN PAPER FORMS Filed Nov; 22. 1967 3 Sheets-Sheet 5 FIGS United States Patent 3,456,355 MICROWAVE DRYER FOR DRYING THE GLUE LINE IN PAPER FORMS William A. Cumming and William J. Bleackley, Ottawa, Ontario, Canada, assignors to Canadian Patents and Development Limited, Ottawa, Ontario, Canada Filed Nov. 22, 1967, Ser. No. 685,192 Int. Cl. F26b /02; H0511 9/ 06' U.S. CI. 341 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a microwave dryer for drying the glue line in multi-sheet paper forms.

Multiple sheet paper forms consisting of several superimposed sheets fixed together along one edge are in widespread commercial use as order forms, invoices, bills of lading, etc. One method of manufacturing these forms is by attaching several, superimposed, travelling strips of webs of paper along or near one edge by means of glue placed between the strips. The width of the strip or web is that of the resultant paper form and the number of superimposed sheets is that of the required copies or duplicates in the form. The travelling multi-layer strip is cut or perforated transversely to the direction of travel to give a series of forms of the required width.

The glue is placed along a line or as a series of dots or blobs between the various sheet at or near what will be the top edge of the form and this line is commonly called the glue line One of the problems involved in this method of fabrication and one that causes a slowdown or bottleneck in the production runs is the time required for drying the glue in the glue line. Ordinary in-air drying is almost out of the question because of the time and space required and bulk drying using R.F. heating ovens has been resorted to. This latter procedure is still relatively slow and holds production well below the speeds and capacities possible by the other components in the overall production apparatus.

It is an object of the present invention to provide a method and apparatus for drying the glue line in multi sheet paper forms rapidly and efficiently.

It is another object of the invention to provide apparatus'for glue line drying that operates at speeds comparable to the production speeds of the other components used in the overall production operation and that can be readily adapted to fit in and operate in conjunction with the other components.

It is another object of the invention to provide glue line drying apparatus that is relatively simple to operate and which does not require a great deal of valuable shop space.

These and other objects of the invention are achieved by a glue line dryer comprising an elongated rectangular microwave waveguide, means for energizing said waveguide at a preselected microwave frequency, and elongated slot cut in one face of the said waveguide, a ridge formed inside said waveguide such as to concentrate microwave energy generally along a line inside the waveguide "ice and adjacent the said slot. The apparatus would be suitably mounted and adapted such that the edge of the travelling paper form strip or web containing the glue line would lie in the region of the waveguide having maximum or near-maximum microwave energy selectively removes the moisture from the glue, drying it almost instaneously without any adverse effects to paper strips themselves.

In drawings which illustrate an embodiment of the invention.

FIGURE 1 is a three-quarter view of a complete dryer.

FIGURE 2 is a view partly broken of a section of the waveguide showing the formation of the ridge,

FIGURE 3 is a three-quarter view of the waveguide drying section and the strip of paper forms passing therethrough,

FIGURE 4 is a cross-section of the ridge waveguide showing the positioning, of the edge of the paper strips including the glue line,

FIGURE 5 is a cross-section of an alternate form of the ridge waveguide,

FIGURE 6 is an internal view of an impedance matching transformer section that may be used, and

FIGURE 7 is a view of a lossless waveguide termination that may be used at the end of the drying section waveguide.

Referring to FIGURE 1, a suitable supporting table 10 with its base 11 carries a magnetron installation 12 with perforated cover 13 for cooling purposes. The output of the magnetron is fed via waveguide bend 14, isolator 15, power level monitor 16, tuner section 17, waveguide bend 18, and microwave transformer section 19 to the Waveguide drying chamber 20. An elongated slot 21 is cut in the front broad face of waveguide 20 and extends around the curved portion of the waveguide such that the edge of a paper strip can be inserted in the slot and can readily travel down the waveguide 20 in the long direction. A series of small ventilation holes 22 are cut in the upper Wall of the waveguide and a manifold 23 encompasses waveguide 21 on three sides and is connected via pipe 24 to a vacuum or suction source.

The magnetron 12 should operate at a frequency selected to give optimum drying action. This frequency would preferably be in the order of 10,000 megacycles. In a device built and tested, however, the frequency of operation was 2450 megacycles and this was found to be satisfactory. Isolator 15 is inserted in the line to protect the magnetron and tuner 17 and monitor 16 are used to tune the system to resonance. These devices as well as the waveguide bends are well known microwave components and particular invention is being claimed for them here as such.

In operation, the drying chamber is energized and tuned to resonance. FIGURE 3 shows the continuous, travelling strip or inch of paper 26 made up of several superimposed sheets being fed to and passing through the drying section. The multilayers or sheets of the paper have between each of the sheets at the upper edge, a line of glue 27 that has been introduced or inserted previously by standard methods at present in use. This glue line as it is usually called is in the wet state and adhesion between the sheets has not been achieved as yet. The paper strip has a series of perforation lines 26a formed thereon to give a series of finished paper forms of the desired width. Only the edge of the paper strip passes inside the waveguide and this is seen more clearly in FIGURE 4. The edge of the paper is inserted through slot 21 into the waveguide 20 and travels inside the opening in U-shaped channel 25. The dimensions of the device are arranged such that the glue line 27 lies generally in the region between slot 21 and the front portion of channel 25. Channel 25 acts not only to guide the paper edge but its outside dimensions are chosen such that the waveguide acts as a ridge waveguide with the microwave energy i.e. the electric field vector being concentrated in the region occupied by the glue line. The theory and operation of ridge waveguides are known in the microwave field and'no particular theoretical discussion is entered into here. For more specific information on these devices as such, reference should be made to Southworth: Principles and Applications of Waveguide Transmission, D. Van Nostrand, 1950, page 134.

The glue is dried selectively by the microwave heating action in that the glue is much more lossy than the paper at the frequency of operation and absorbs all or nearly all of the heating and drying energy. The system is operated as a resonant circuit and, therefore, there is no need for a dissipative termination or load to absorb excess energy at the end of the waveguide. Resonance does result in standing waves being formed along the length of the drying waveguide section but as the paper travels in this direction there is an overall averaging effect with little or no chance of burning or damage to the paper.

The heating and drying of the glue causes vapours to be formed but these can emerge from the waveguide via holes 22 and be drawn or sucked away through manifold 23 and pipe 24.

In the above description, the waveguide drying section is shown with the waveguide rectangular in cross-section. The device would work with a circular cross-section waveguide, provided it incorporates .a ridge similar to the one described above. Such waveguides are usually referred to as fin line or fin loaded waveguides. In addition to a circular cross-section, a rectangular waveguide having a different cross-section might be used. FIGURE shows such a guide 28 in cross-section, which has in wardly projecting channels or ridges 29 and 30. The paper web 26 travels in the slot 31 with the glue line 27 lying in the waveguide in the region of concentrated drying energy.

FIGURE 6 shows transformer section 19 in more detail. This device is required to match the high impedance standard waveguide to the ridge waveguide of the drying section. The device comprises a smoothly tapering insert 32 inside section 19 that becomes integral with ridge 25 inside drying section guide 20.

Normally the waveguide drying section can be terminated by a flat plate over the end of the guide. It has been found that there is a possibility of sparking at this point and it is preferable to terminate the guide as shown in FIGURE 7 with a tapering end 33 to the ridge shown with an opening or slot 34 for guiding the edge of the paper strip.

The glue line dryer described above can be fitted into existing paper form production apparatus most readily and can operate at speeds comparable or even better than their speeds. The glue injecting and paper transport mechanisms exist and need not be described here. A protective device to switch oif the magnetron on stoppage or breakdown of the paper transport would probably be required but this can be readily devised and does not form part of the glue dryer system as such.

In a glue dryer built under shop production conditions drying was effective at paper speeds of 400 f.p.m. and higher speeds could be accommodated without difliculty.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A microwave dryer for drying the glue line in multisheet paper forms comprising:

(a) an elongated rectangular waveguide section,

(b) a magnetron connected to said waveguide section to energize it at a microwave frequency,

(c) waveguide tuning means inserted between waveguide section and magnetron to tune the waveguide to resonance,

((1) an elongated slot cut in one broad face of the rectangular waveguide, and

(e) an elongated channel member of generally U- shaped cross-section positioned inside of said waveguide with the open portion facing towards the said slot, said channel member being positioned and of such outside dimension as to cause the waveguide to act as a ridge waveguide with the microwave energy being concentrated in the region between the slot and the elongated channel member.

2. A microwave dryer as in claim 1 wherein the said slot and the opening in said channel member are positioned in relation to each other such that the edge of a rapidly moving strip of multisheet paper forms can readily pass down the slot in its long direction with the glue line of the forms lying in the area of concentrated microwave energy for a sufficient length of time to dry the glue in the glue line.

3. A microwave dryer for drying the glue line in multisheet paper forms comprising:

(a) an elongated ridge waveguide section, said waveguide adapted to have an internal region of concentrated microwave energy,

(b) an elongated slot in one face of said waveguide section such that the edge of the multisheet paper form containing the glue line may be inserted in the waveguide with the glue line lying generally in the region of concentrated microwave energy,

(c) means for energizing said waveguide section at a microwave frequency,

(d) means for tuning the waveguide to resonance, and

(e) said ridge waveguide having an internal elongated structure protruding from the wall of the waveguide opposite said slot into the central region of the waveguide and of such dimensions as to provide an elongated region of concentrated microwave energy adjacent the slot.

References Cited UNITED STATES PATENTS 3,197,601 7/1965 Wayne et al. 219l0.55 3,293,765 12/1966 Winkler et al. 34-1 3,384,814

U.S. Cl. X.R. 219-1055 

